The present invention relates generally to films and other articles that incorporate information whose appearance is highly dependent upon viewing angle.
Films that incorporate directional imagesxe2x80x94images that are viewable at some viewing geometries and not othersxe2x80x94are generally known. U.S. Pat. No. 6,024,455 (O""Neill et al.), for example, discloses reflective articles in which a multilayer film covers a patterned retroreflective layer. The patterned retroreflective layer can include an indicia layer having patterned regions comprising conventional inks, dyes, or other substances which are substantially opaque to some wavelengths but transparent to others. Such films, however, require specialized lighting arrangements for optimal viewing.
PCT Publication WO 99/36258 (Weber et al.) discloses, among other things, color shifting films with printed indicia, and optical brighteners such as dyes that absorb in the UV and fluoresce in the visible region of the color spectrum. Such articles can also provide images whose appearance changes with viewing geometry, particularly where the printed indicia is provided on a back side of the color shifting film with respect to an observer. Advantageously, such articles can be viewed under ordinary diffuse lighting conditions, such as in a typical office environment.
In the search for always different and visually impressive product constructions, applicants have discovered new and useful combinations of color shifting films and fluorescent colorants. For example, applicants describe herein embodiments in which at least a first and second colored portion are disposed behind a color shifting film, such portions comprising respectively first and second different fluorescent colorants. The first and second colored portion define indicia. The properties of the color shifting film and of the first and second fluorescent colorants can be selected so that at a first angle fluorescent emission from only the first colorant is visible through the film. At a second angle, fluorescent emission from the second colorant is visible through the film. If fluorescent emission from the first colorant is not visible through the film at the second angle, a third angle may exist at which fluorescent emission from both colorants are visible through the film. A fourth angle may also exist at which fluorescent emission from neither colorant is visible through the film. By arranging the first and second colored portions as a foreground and background of the indicia, these properties can produce highly visible indicia with dramatic contrast changes as a function of angle.